Process for producing a drip irrigation conduit

ABSTRACT

A process and an installation for producing a drip irrigation conduit having discrete internally located emitter units bonded at axially spaced apart locations of an internal surface thereof, wherein the irrigation conduit is continuously extruded from an extrusion cross head at a first outer diameter and a first linear velocity and is drawn off through a calibrator unit to a second and lesser outer diameter at a second and greater linear velocity greater than the first linear velocity, the emitter units being continuously supplied on a carrier member which extends from within the extruder cross-head to the region of an inlet of the calibrator unit. While so supported the emitter units are accelerated so as to attain an emitter unit linear velocity substantially equal to said second linear velocity and are displaced at this velocity into contact with the extruded conduit where the latter has substantially attained its second linear velocity and therefore continue to be displaced while still supported in contact with the extruded conduit until the emitter unit is heat welded.

This is a continuation, of application Ser. No. 08/001,316, filed Jan.6, 1993, now abandoned which in turn is a continuation of Ser. No.07/895,543, filed Jun. 8, 1992, now abandoned which in turn is acontinuation of Ser. No. 07/628,172, filed Dec. 14, 1990, now U.S. Pat.No. 5,122,044, which in turn is a divisional of Ser. No. 07/412,889,filed Sep. 26, 1989, now U.S. Pat. No. 5,022,940, which in turn is acontinuation of Ser. No. 07/211,372, filed Jun. 24, 1988, now abandoned.

FIELD OF THE INVENTION

This invention relates to the introduction of elements into a plastictube during the extrusion thereof and the bonding of these elements tothe inner surface of the tube at predetermined locations. The inventionrelates particularly to a process and an installation for producing adrip irrigation conduit having discrete internally located emitter unitsbonded at axially spaced apart locations of an internal surface thereof.

BACKGROUND OF THE INVENTION

The enclosing or encasing of cylindrical objects during the course ofthe extrusion of a plastic sleeve has long been known, e.g. in theproduction of covered cables or the like. Furthermore it is known tointroduce discrete cylindrical objects into a tube during the course ofthe extrusion thereof. Thus, for example, in U.S. patent Ser. No.2,484,965 (Slaughter) there is disclosed a method of making extrudedcollapsible tubes which essentially consists of extruding a continuoustube by means of an extrusion cross head and successively feeding intothe extrusion successive spaced-apart tube closures so that the tube isformed around the closures. Similarly, in U.S. patent Ser. No. 2,575,138(Slaughter) there is disclosed a process for packaging cylindricalarticles within a continuous tube comprising the steps of extruding thetube by means of an extrusion cross head, successively feeding thearticles to be packaged through the cross head so as to be enclosed bythe tube, the portions of the tube between the successive enclosedarticles being subsequently sealed and severed.

In both cases the tube is extruded by an angular extrusion nozzle (knownas an extrusion cross head) with the cylindrical objects beingsuccessively fed into the cross head by means of an appropriate pushermechanism.

In completely analogous fashion there is disclosed in U.S. Pat. No.3,981,452 the application of this known process in the production of anirrigation conduit in which are located at predetermined intervals,successive cylindrical units which together with the inner surface ofthe conduit form a plurality of emitter units.

In all cases of the prior art referred to above, the element to beenclosed by the extruded tube, whatever its nature, is of cylindricalshape and is wholly enclosed by the extruded tube.

The present invention, on the other hand, relates particularly to theproduction of a drip irrigation conduit, wherein the internally bondedemitter units are not of circular cross section extending across theentire periphery of the surrounding conduit, but are of limited depthwith the bonded area thereof extending into the conduit for less thanhalf the diameter thereof. Drip irrigation conduits having emitters ofthis kind are, for example, disclosed in our earlier U.S. Pat. No.4,307,841.

SUMMARY OF THE INVENTION

It is an object of the present invention to provide a new method andapparatus for the production by extrusion of drip irrigation conduitshaving internally heat welded emitter units of this kind.

According to one aspect of the present invention, there is provided aprocess for producing a drip irrigation conduit having internally heatwelded emitter units, the welded area of each emitter unit having atransverse, peripheral extent not greater than half the transverseperipheral extent of the conduit, comprising the steps of:

continuously extruding an irrigation conduit from an extrusion crosshead at a first outer diameter and a first linear velocity;

passing the extruded conduit through an intermediate zone and into acalibrator unit so as to be drawn down to a second outer diameter whichis less than the first outer diameter and so as to have a second linearvelocity greater than the first linear velocity;

supporting said emitter units over a support region coaxial with theextruded conduit and extending from a first end thereof within theextruder cross-head to an opposite end thereof within the calibratorunit;

successively accelerating said supported emitter units so as to attainan emitter unit linear velocity substantially equal to said secondlinear velocity;

displacing each supported emitter unit at said emitter unit linearvelocity into contact with said extruded conduit where the conduit hassubstantially attained said second linear velocity;

displacing each supported emitter unit in contact with the extrudedconduit until the emitter unit is heat welded to the conduit atsubstantially said opposite end;

cooling the extruded conduit and internally heat welded emitter units;

successively determining the location of the heat welded emitter unitsin the conduit; and

aperturing the conduit so as to form respective drip outlets for theemitter units.

According to another aspect of the present invention there is providedan extrusion installation for use in carrying out this process andcomprising:

an extrusion cross head with an axial bore;

a calibrator unit spaced therefrom by an intermediate region;

drawing-off means located downstream of said calibrator unit for drawingoff the extruded conduit through and out of the calibrator unit at aconduit linear velocity;

an emitter carrier element located coaxially with said axial bore havinga first end located within said bore and a second opposite end locatedwithin said calibrator unit;

emitter feed means for successively feeding emitter units to saidcarrier element; and

emitter displacement means for successively accelerating said emitterunits along said carrier element so as to attain an emitter unitvelocity substantially equal to said conduit linear velocity, fordisplacing said emitter units along said carrier element at said emitterunit velocity in contact with an extruded conduit when the latter hassubstantially attained said conduit linear velocity and displacing saidemitter units along said carrier element until the emitter units areheat welded to the conduit at substantially said opposite end of saidcarrier element.

By virtue of the process and apparatus in accordance with the invention,it is possible to ensure that the extruded conduit is contacted, whilststill in a semi-molten malleable state, by successive emitter unitswhich are welded to the conduit when the latter has substantiallyattained its second linear velocity, thereby ensuring that the effectiveheat welding of the emitter units to the conduit takes place as part ofthe overall extrusion process without disturbing the extrusion processor overall characteristics of the conduit.

SUMMARY OF THE DRAWINGS

For a better understanding of the present invention and to show how thesame may be carried out in practice, reference will now be made to theaccompanying drawings in which:

FIG. 1 is a schematic view of a drip irrigation conduit extrusioninstallation in accordance with the present invention;

FIG. 2 is a longitudinally sectioned view, on an enlarged scale, of aportion of the installation shown in FIG. 1;

FIG. 3 is a cross-sectional view of the installation shown in FIG. 2taken along the line III--III; and

FIGS. 4a and 4b show cross-sectional views of various modifications of adetail of the installation shown in FIGS. 2 and 3.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENT

As seen in FIG. 1 of the drawings, the installation comprises anextruder 1 provided with an extrusion cross head 2 having a coaxial bore3 through which extends an elongated emitter carrier 4. An upstream end4a of the carrier 4 is juxtaposed with respect to an emitter stack 5from which emitters 6 can be successively fed on to the upstream end ofthe carrier 4.

A calibration and cooling unit 8 is located downstream from theextrusion cross head 2 and is spaced therefrom by an intermediate region9. A downstream end 4b of the carrier 4 projects into the unit 8.Downstream of the unit 8 are a plurality of further cooling units 10followed by a conduit aperturing station 11, caterpillar type drawingoff means 12 for drawing off an extruded conduit 13 and a conduitcoiling mechanism 14.

An emitter displacement means 16 is located upstream of the upstream end4a of the carrier 4 and is provided with a pusher 17 aligned with thecarrier 4. The displacement means can be, for example, mechanically,electro-mechanically, or hydraulically operated so as to displace thepusher 17 at a rate which is at all times controlled in accordance withoperational requirements.

Reference will now be made to FIGS. 2 and 3 of the drawings for a moredetailed description of the extrusion cross head 2, the carrier 4 andthe calibration and cooling unit 8. The extrusion cross head 2 comprisesa mandrel 21 having an outwardly directed flange 21a screw bolted to acylindrical sleeve 22 in which is screw fitted a die element 23, therebeing defined between the die element 23 and the mandrel 21 a spacingfrom which is extruded the conduit 15.

Spaced from the extrusion cross head 2 by an intermediate region 9 isthe calibrator and cooling unit 8 comprising an apertured calibratortube 24 formed integrally with the calibrator flange 25 which is securedto the walls of the unit 8, the latter being filled with cooling waterunder a vacuum.

Extending through the axial bore 3 of the extrusion cross head 2, theintermediate region 9 and into an axial bore 26 of the calibrator tube24 is the elongated carrier 4 which, as seen in FIG. 3 of the drawings,is formed with a pair of elongated ducts 27 which pass along the lengthof the carrier and serve for the passage of cooling water from an inletnipple 28.

The carrier 4 is formed with an upper, axially directed rib 29 adaptedto fit into a corresponding recess formed in a base of an emitter 6 soas to support and align the latter. The carrier 4 is supported at theupstream end 4a thereof by a support column 30.

In operation, plastic material 31 passes from the extruder 1 into theextrusion cross head 2 so as to emerge therefrom at a first linearvelocity as an extruded, wide diameter, molten conduit 13. Under thetraction force exerted by the drawing-off means 12, the conduit 13passes through the narrower opening of the calibrator tube 24 with itsdiameter and wall thickness being reduced to substantially their finaldimensions and at a second and higher linear velocity. As the extrudedconduit 13 passes at this second linear velocity through the calibratorunit 8 and subsequent cooling units 9 it cools down until it reaches itsfinal set state.

At the same time, successive emitters 6 are fed on to the upstream end4a of the carrier 4 and are displaced by the pusher 17 along the carrier4 which serve to guide the emitters, so as to be accelerated up to alinear velocity substantially corresponding to the second linearvelocity of the conduit until the upper surface of each successiveemitter 6 contacts a spaced apart, inner surface location of the conduitwhen the latter is still in a semi-molten state in the region of aninlet to the calibrator unit 8 and when the conduit has substantiallyreached its second linear velocity. Each emitter 6 thus begins to becomeheat welded to the inner surface of the conduit whilst being displacedalong the carrier at a linear velocity substantially equal to the secondlinear velocity of the conduit until, by the time the emitter hasreached the end of the carrier, it is firmly heat welded to the conduit.

The displacement of the emitters 6 by the pusher 7 can be effecteddirectly or indirectly, in the latter case via one or more intermediateelements or emitters.

It can be seen that at all times the carrier element never contacts theextruded conduit and supports the emitters at surfaces thereof remotefrom those surfaces of the emitters which are ultimately heat welded tothe conduit.

The spacing apart of the emitters 6 within the conduit 13 is determinedby time intervals between the successive displacements of the emitters 6along the carrier 4.

Once the emitters 6 have been firmly heat welded to the conduit 13 andafter the latter has emerged from the final cooling unit 9, the locationof the emitter units 6 within the conduit 13 are sensed and the conduit13 then passes the aperturing station 11 where it is apertured inpositions corresponding to the emitter outlets. The conduit 13 with theinternally heat welded emitters drawn off by the drawing-off mechanismis coiled by the coiling mechanism 14.

Whilst in the embodiment shown in FIGS. 2 and 3 of the drawings thecarrier 4 is so constructed as to have the emitter units 6 supportedthereby and aligned thereon (further embodiments illustrating this beingshown in FIGS. 4a and 4b of the drawings), the carrier construction canbe so designed that emitter units are effectively suspended from andaligned by the carrier.

Furthermore, whilst in the embodiment specifically described above thecarrier 4 projects into the calibrator unit 8 so as to ensure thatcontact between the emitter units and the extruded conduit and the fullheat welding thereof take place when the latter has achieved its finalsubstantially constant velocity, the carrier 4 may extend only to theregion of the inlet of the calibrator unit 8. This situation is lessideal as far as the ultimate quality of the product compared with thatdescribed in detail above wherein it is ensured that the heat welding ofthe emitters 6 to the conduit 13 does not result in undue stressing ofthe conduit and does not interfere with the stability of the extrusionprocess or with the quality of the extruded conduit.

I claim:
 1. A process for producing a drip irrigation conduit having atransverse peripheral extent and having internally heat welded emitterunits, each emitter unit having a welded area which has a transverse,peripheral extent which is not greater than half the transverseperipheral extent of the conduit, comprising the steps of:continuouslyextruding and irrigation conduit from an extrusion cross-head at a firstouter diameter and a first linear velocity; passing the extruded conduitthrough an intermediate zone and into a calibrator unit so as to bedrawn down to a second outer diameter which is less than the first outerdiameter and so as to have a second linear velocity greater than thefirst linear velocity; guiding said emitter units with respect to aguide region within the extruded conduit and extending from a first endof said guide region within the extruder cross-head to an opposite endthereof within the calibrator unit; displacing each guided emitter unitinto contact with the extruded conduit; firmly heat welding each emitterunit to the conduit when the latter has substantially attained saidsecond linear velocity; cooling the extruded conduit and internally heatwelded emitter units; successively determining the location of thewelded emitter units in the conduit; aperturing the conduit so as toform respective drip outlets for the emitter units.
 2. The process ofclaim 1, wherein each emitter unit comes into contact with said extrudedconduit where the latter has substantially attained said second linearvelocity.
 3. The process of claim 1, wherein said calibrator unit isprovided with an inlet and the opposite end of said guide region islocated in the region of said inlet of the calibrator unit.